Most modern commercial aircraft make use of high bypass jet engines that include a number of rotating fan elements. The rotating fan elements include low speed rotating components, such as used in compressor bearings, as well as high speed rotating components, such as used in turbines. Unfortunately, during in-flight operation both the low speed rotating system and the high speed rotating system can introduce unwanted engine vibrations. Reduction of engine vibrations is important for a variety of reasons. During in-flight operation, engine vibration may result in excessive cabin noise. The cabin noise and/or resulting introduction of physical vibrations into the body of the aircraft may in turn cause passenger and crew discomfort. Over the long term, such engine vibrations can significantly increase the maintenance costs and reduce the life cycle of a jet aircraft.
Engine vibrations are typically created by small variations in the fan blade configurations which cause an imbalance in the rotating systems. As such, it has been known for some time that balancing techniques can be used to reduce engine vibrations. Using these techniques, which are quite analogous to the balancing of an automobile tire, weights of a specific mass are placed at specific locations In the rotating system. By carefully placing such weights engine vibration can be reduced considerably.
In order to determine the specific locations and weights required to balance a jet engine there have been developed a line of instrumentation units known variously as airborne vibration monitoring systems. The primary purpose of these systems is to measure and record engine vibration levels, as detected from analog vibration signals produced by engine mounted accelerometers. Vibration signals may be gathered during an engine balancing operation on the ground or in other instances may be taken during in-flight operations. Vibration amplitudes are typically recorded in narrow frequency bands synchronous with signals indicated by engine speed tachometers.
In fact, a number of sophisticated computer and digital signal processing systems have been developed for processing the accelerometer and tachometer signals for high accuracy solution of the balance equation. These systems are not entirely satisfactory however. In particular, although they may accurately measure in-flight vibration data and rapidly calculate a balance solution, they typically require access to a separate computer terminal or portable personal computer. It is, however, logistically difficult for maintenance personnel who are typically working in an aircraft hangar or along an active airport runway to locate, set up, and use such equipment effectively. The environment is dirty, noisy, hectic, and may be exposed to the weather. Such an environment is therefore not typically conducive to the effective use or even the easy availability of separate computer equipment. It is desirable, therefore, for such a system to take into account the physical working conditions of the personnel who are most often expected to use the equipment.
Furthermore, existing systems typically calculate a balance solution and then display this as a raw indication of phase angle and the size of the weight required. However, it is common for weights to already be installed on certain fan blades. It would therefore also be desirable if such a system took into account the typical information requirements of engine maintenance personnel.
The system should in particular consider that maintenance personnel may not always be prepared to easily deal with a raw mathematical solutions, and would rather prefer to be instructed what to do in a way in which they most often think, which is in terms of mechanical part installation and configurations.